In the field of astronomy in the mid-60s, quasars were very sexy objects – gigantic, star-like masses about which little was known. I was a graduate research student at Cambridge working towards my PhD, and chose quasars as the subject for my thesis. Part of my project involved surveying the sky for them using a radio telescope.

There weren't many computers around then, and the data scrolled out of the machine as a line in red ink on chart paper – 96ft of it every day – which I'd then spread over a table and examine. As well as quasars, the telescope picked up "artificial interference" – cars, arc welders and pirate radio stations could all make their presence felt. But every so often, a third type of signal appeared, something that didn't seem to fit into either category.

After I'd logged it a few times with a question mark, I realised this unclassifiable squiggle had been appearing regularly, if intermittently. I alerted my thesis supervisor, Tony Hewish. In order to examine the signal, we decided to run the chart paper faster to spread out the recording. As the paper flowed under the pen, a steady pulse started to appear. The source didn't seem to be man-made – it was moving around with the stars, keeping pace with the constellations. We estimated it was 200 light years away, far beyond the sun and planets, but still within our galaxy, the Milky Way.

A new possibility presented itself: artificial intelligence. For a while, my discovery was called LGM-1, which stood for "Little Green Men". Without a solid explanation, we couldn't categorically rule out ET – at least, until I found a second mysterious signal. The possibility of two lots of aliens trying to make contact on the same frequency simultaneously seemed too remote.

That second discovery almost didn't happen. I'd found another squiggle, and went to the observatory at 3am when it was due to pass by our telescope again. But because the night was so cold, the machine had malfunctioned. A combination of switch-flicking, cursing and blowing brought the apparatus back to life, but for only five minutes. The pen leapt again on the paper – blip, blip, blip – a different rate, but clearly the same kind.

This was the "Eureka!" moment. Wading through miles of chart, I discovered two more of the mysterious signals. I had, it transpired, discovered the first four examples of an unimagined kind of star – bizarre astral bodies that transmitted radio beams as they spun, which swept through space like the ray of a lighthouse. We called them pulsars.

The paper detailing the discovery was published, and the press descended. It was clear they didn't know how to handle a young woman scientist. Photographers would say, "Could you undo some buttons on your jacket, please?" Journalists asked how many boyfriends I had.

I finished my thesis on quasars – it was too late to change the title – but added an appendix detailing my discovery. Tony and a colleague, Martin Ryle, later became the first astronomers to receive a Nobel prize, partly for their pulsar work. It doesn't much bother me that my name wasn't included; in those days students weren't recognised by the committee.

Still, very few people get the chance to make mega discoveries, and it's thrilling that mine opened up a whole new area of astrophysics. Thirty years on, pulsar astronomy is a field that refuses to mature. It behaves like an energetic child, constantly delivering surprising results, and is great fun for that reason. Pulsars are in an ideal part of the universe to test Einstein's theory of relativity – so far, it's holding up well. They may even one day act as navigational beacons for spacecraft. I'll never tire of them; they really are the most extraordinary objects. For example, the material they're made of is so dense, a thimbleful would weigh the same as every living human being put together.

One of the hazards of making a major discovery early in your career is the burden of expectation, not helped in my case by becoming a wife and mother soon afterwards. I'm sure some people think it was a flash in the pan. But I'm now in my 60s – and I'm still in this fascinating, dynamic field. Without my discovery, I might easily be running the local WI.